There are many types of shutting systems for closing a bay, separating a room or covering a swimming pool, etc. Fast roll-up doors comprise a flexible curtain suitable for being wound or unwound about a winding axle at high speed, allowing apertures of large dimensions to be opened and shut in a very short time. They are particularly suitable for closing apertures between two rooms or between a room and the outside in warehouses, workshops, shops, laboratories, and the like. In order to ensure structural stability, the lateral edges of such curtains are coupled to guiding rails fixed to the lateral walls defining the lateral edges of the aperture. The lateral edges of the curtain can freely slide along the guiding rails during winding and unwinding but are held by the rails unless exposed to an unexpected pull-out force, Fpo, of sufficient magnitude to de-couple the curtain edges from their corresponding guiding rails. For example, the lateral edges of the curtain may be provided with a bead and be inserted through a slit running along a corresponding guiding rail such that the bead can freely move along the rail, but cannot pull-out through the slit unless exposed to a pre-determined pull-out force, Fpo. The bead can be continuous or discontinuous, forming teeth like in a zip (cf. e.g., WO2008/155292 and WO9220895). Some doors are provided with means for automatically driving the pulled-out curtain edge back into the rail. Such re-insertion system is disclosed e.g., in WO2008/155292.
Roll-up doors can be exposed to many external aggressions, such as wind (in case they separate indoor from outdoor), accumulated rain and snow (in case the curtain is not held vertically); impacts with vehicles in movement, static obstacles placed in the closing trajectory of the curtain, and the like. Because such roll-up doors may have rather large dimensions, even a moderate pressure applied on one side of the curtain, such as by wind, can generate forces of high magnitude which are transmitted to the lateral edges of the curtain and to the coupling between lateral edges and guiding rails. In the best of cases, friction between the lateral edges of the curtain and the guiding rails may, as a consequence, be created thus hindering the winding and unwinding speed of the curtain and increasing wear rate. In the worst of cases, such forces may prevent the proper closing of the curtain. If the motor controlling the rotation of the un-winding drum is not stopped as soon as the bottom edge of the curtain is substantially hindered or fully prevented from moving forward along the guiding rails, severe damages may occur to the door. It is therefore important to control the instantaneous speed of the curtain and identify any abnormality in the closing sequence to preserve the roll-up door from any severe damages.
WO2009/090097 discloses an object-detection mechanism which is programmed to stop the closing of a gate in case an object is detected in the closing-trajectory of said gate. The object-detection mechanism comprises light emitters and light receptors with light reflectors allowing the scanning of the area of the aperture comprised between the two guiding rails through a pattern of optical rays crossing from one guiding rail to the other. Such system is only useful for the detection of an obstacle in the trajectory of the curtain, but is ill fitted for detecting any other malfunctioning of the roll-up door, such as for example a lateral edge pulling out of the corresponding guiding rail because of a strong wind.
In DE10 2005 003794 a light barrier of the same type as the foregoing system detects obstacles. The light barrier also monitors the advancement of the bottom edge of the curtain as it moves from one light barrier to the next. In order to have a fine monitoring of the position of the bottom edge of the curtain, a dense network of optical rays is required for forming a ‘barrier’, which increases the cost of the device.
EP2441911 discloses a system for monitoring the instantaneous speed and position of a curtain comprising an optical detection system monitoring the passage rate of discontinuous beads forming a zip used for holding the lateral edges of a curtain in a corresponding guiding rail, as discussed above. The system comprises a light emitter facing one main surface of the curtain at the level of the zip-teeth at a lateral edge thereof, and a light receptor transmits a signal to a CPU each time an emitted light ray passed across the curtain through a space separating two adjacent teeth. Such system is very efficient as long as the teeth forming the discontinuous beads are in perfect state. With wear and use, a tooth can be deformed or can fall, so that the space between two adjacent teeth is not constant anymore, yielding a wrong interpretation of the presence of a problem with the curtain, which actually does not exist. Indeed, curtains provided with a discontinuous bead at their lateral edges can continue to function very satisfactorily even if a few teeth are missing. The speed detector, however, cannot.
There therefore remains a need for a durable, reliable, and cost effective solution for monitoring the instantaneous position and speed of a curtain of a roll-up door system. The present invention proposes a solution to such problem. This and other advantages of the invention are described more in detail in the following sections.